Conventional linear bearing systems are widely used in various industrial applications that require motion between at least two parts. The linear bearing system typically includes an axially extending guide rail having rolling grooves in outer surfaces and a slider mounted over the guide rail. The slider includes a slider body and an end cap fitted at both ends of the slider body. The slider includes rolling elements disposed therein. The rolling elements, such as, for example, steel balls, are loaded in the circuits. Before an object connected to or supported by the slider can move, force has to be applied to the object until the resisting force due to static friction is overcome. This static friction is also called “stiction”.
Once the object starts moving, the resisting force drops to a lower level dynamic friction force due to friction. The sudden reduction in the resisting frictional force causes the object to accelerate rapidly or “jump”. This jumping action prevents the smooth acceleration of the object from other components operably connected with one another thereby presenting problems for moving the object a small distance as it tends to jump past the intended stopping point.
In the linear bearing systems that are heavily loaded but remain stationary for long periods of time, there is the possibility of the bearings being damaged by “false brinelling”, a condition where the load on a stationary rolling element is large enough to cause the element, over time, to permanently deform (dent) the race surface. As appreciated by those skilled in metal arts, “false brinelling” is damage caused by fretting, which causes imprints. These imprints look similar to “brinelling” thereby resulting in permanent material deformation. The basic cause of “false brinelling” is a lubricant, which is pushed out of a loaded region. Without the lubricant, wear is increased and the resulting wear debris may oxidize and form an abrasive compound, which further accelerates wear. In normal operation, a rolling-element bearing has the rollers and races separated by a thin layer of the lubricant, i.e. grease or oil. Although these lubricants normally appear liquid, under high pressure they act as solids and keep the bearings and the race from contacting one another.
If the lubricant is removed, the bearings and the races can contact directly. While bearings and races appear smooth to the eye, they are microscopically rough. The bearing load is thus spread over much less area increasing the contact stress, causing pieces of each surface to break off or to become pressure-welded then break off when the bearing rolls on. One method of preventing “false brinelling” is to move the object, or rotate the shaft, periodically, which is inconvenient or even impossible in certain application thereby resulting in total replacement of the bearing assembly.
There are numerous other prior art methods of static friction reduction in linear hearing applications. One of such methods is used in a pressurized air bearing applications. In the air bearing application, compressed air lifts the object from the bearing surface so the only friction is between a gas and the bearing surfaces. Such method requires a very flat, clean, and smooth surface, a source of clean dry compressed air, seals to keep the gas from escaping. If the air supply is stopped while the object is in motion, the bearing is usually damaged and has to be replaced.
Another method is used in a pressurized oil bearing application. Such method also requires a very flat, clean, and smooth surface, a source of clean oil, seals to keep the oil from escaping. The friction between the oil and the bearing surface is higher than with an air bearing and results in the bearing being damaged and subject to be replaced.
The art is replete with various methods and designs aimed to lubricate the sliders as the sliders move along the rails in linear bearing systems. One of such prior art patent is U.S. Pat. No. 5,678,927 to Yabe, et al., which teaches a linear guide apparatus including a guide rail, a slider fitted movably to the guide rail, a plurality of rolling elements loaded to move the slider relative to the guide rail. A seal device is mounted on a side of the slider to seal a clearance existing between the guide rail and the slider, the seal device includes a lubricant-containing polymer member that is fitted into the recess and has an inner sealing portion slidably contacting the guide rail and an outer surface opposed to the inner sealing portion and positioned at a predetermined clearance relative to the recess.
U.S. Pat. No. 5,678,927 does not teach a system or method that prevents “false brinelling”. Should the linear guide apparatus be subject to “false brinelling”, the apparatus or at least some of the components will need to be replaced, which is not cost effective and may require to stop or delay manufacturing process of industrial application wherein the linear guide apparatus is used.
Another prior art reference, U.S. Patent Application Publication No. 2004/0234176 to Sattler et al., discloses another design of a linear rolling bearing element comprising a carrier body that is mounted through rolling elements for sliding on the running surface of a guide rail, and, for forming a rolling element circuit, a load-bearing zone and a return channel, which extends parallel to the direction of movement of the linear rolling bearing element. The load-bearing zone and the return channel are connected to each other through deflecting channels that are arranged on the carrier body in frontally adjoining head pieces that contain lubricant ducts starting at a filling point of each head piece and leading to the rolling elements.
Similar to the U.S. Pat. No. 5,678,927, the Sattler et al. reference does not teach a system or method that prevents “false brinelling”. The linear rolling bearing element does not allow redistribution of lubricant in bearings that remain static for long periods of time. Should the linear rolling bearing element be subject to “false brinelling”, at least some of the components of the linear rolling bearing element will need to be replaced, which is not cost effective and may require to stop or delay manufacturing process of industrial application wherein the linear rolling bearing element is used.
Hence, there is a need for an improved linear bearing assembly and methods that will prevent “false brinelling” and provide for improved redistribution of lubricant in bearings that remain static for long periods of time. The inventive concept as set forth further below improves the aforementioned prior art systems and methods.